Automatic telephone-exchange system



Dec. 29, 1925 1,567,122

' B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Oct. 5, 1904 7shets-Sheet l Zgc V) fuif m76, /zp

Y H /oi vez? 730 I//ITNESSES: Y JNI/ENTOR.

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*7A/@Jim ATTORNEY.

Dec. 29,1925. 1,567,122 B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEMFiled Oct. ,5, 190g '7 Sheets-Sheet 2 d, u s l xm B. G. Du nham,WTNESSES. Q' [Nl/ENTO.

Dec. l 29 1925- 1,557,122

- B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed oct. 5, 1904''7 sheets-sheet \B. .Dunha WITNESSS: by N a NVENTUR.

m l ATTORNEK- Dec. 29, 1925- 1,567,122

B. G. DUNHAM AuTom'rIc TELEBHONE EXCHANGE SYSTEM Filedoct. 5, 1904 7sheets-sheet 4 Y B54. Dunham 2\ D WHW/isms: L; 3 m IN1/zwom dm! 508V,e5( 7AM .ffm/aver.

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Dec. 29, 1925 1,567,122

B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SY\SIEM Filed Oct. 5, 1904 '7Sheets-Sheet 5 Q f? Q Q {Qx Q QL" Q Q. B S n l .(Dunhmfn, WIT/vgsw; zg tINVENTOR.

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Dec. 29, 1925- 1,567,122 B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGESYSTEM Filed Oct. 5, 1904' 7 Sheets-Sheet 7 WIEEEEEE: 'Inval-lfm:Ei-Emblem' switch involved in the connection are, or are adapted to be,connected in abridged path across the circuit of the respectivesubscribers lines, and trunk lines, instead of being connected in seriesin the talking circuit, as has been the case in most systems of theprior art. Furthermore instead of these bridges being all closed acrossthe talking circuit of an established connection, a part ofthe bridgesare open after the corresponding selecting switches have performed theirselecting functions and established the con iiection. Thus it will beseen from Fig. 1 that the controlling magnets, VR and RR, of the firstselector of the calling line, and VR and RR', of the second selector,are disconnected from the talking circuitv built up between the twosubscribers lines shown, although these magnets were present in bridgesacross the circuit long enough to enable them to control theircorresponding selectors in selecting and connecting with the propertrunk lines. In this way the disadvantage in the old system of havingthe series magnets in the talking circuit is eliminated, and while thebridge system is adhered to, the disadvantage of having too many sets ofmagnets bridged across the talking circuit is eliminated.

An understanding of the circuits of the snbscribers station adapted foruse with my invention may be had by reference to Fig. 2. The talkingapparatus, consisting of a receiver, transmitter and induction coil, maybe connectedrbetween the vertical and rotary limbs of the lines, V andR, respectively, by the action of the hook switch, 3, in a manner wellunderstood. Under normal conditions, that is, when the receiver is uponthe hook, the bell or ringer, 4. is connected between the two sides ofthe line, thisV connection eX- tcnding through the spring, 5, and thearm, (i, of the hook when the telephone is not in use. vVhen thereceiver is removed from the hook this connection is broken, and thetalking contacts completed in an obvious manner. All ground connectionsat the sub` scribers station are primarily controlled at the pair ofcontacts, .7, these contacts being held open as long as the receiver ison its hook, and after the receiver has been removed, until the impulsetransmitting device has been put into operation.

The impulse transmitting device acts by causing the springs, 3 or 9, toengage the ground spring, 10, according to whether impuises are to besent over the vertical or rotary sides of the line. That is, if siximpuises are to be transmitted, the spring 8, will be pressed againstthe spring, 10, siX times, thus allowing that many impulses to Atow fromthe central oiiice over the vertical :ei-de of the line to ground. 1t isobvious from the presence of the springs, 7, that no such impulse cantake place unless the receiver has been removed from its hook, and

manner an impulse over the rotary side of the line may be secured bypressing the spring, 9, against the spring, 10. It should be rememberedthat all selecting is done over the vertical side of the linel bysending a series of impulses corresponding to the digits belonging tothe number of the subscriber wanted. Each series of impulses over thevertical side of the line caused by the movements 'of the spring, 8, isfollowed by a single impulse over the rotary side of the line caused bythe movement of the spring, 9.

When the hook, 3, is depressed at the close of the conversation, itsarm, 11, serves to press the springs, 12, 13 and 14, momentarily intoengagement with each other, thereby grounding both the vertical androtary sides of the line through the spring, 14, and the contact, 7. Themechanical arrangement of parts is such that the springs, 1Q, 1.3, and14, are not brought into engagement with each other as the hook rises,or while it is either depressed or elevated.

15 is the spring actuated by the ringing lntten, this'spring normallybearing against spring, 16, and serving to hold closed the talkingcircuit. When, however, the ringing button is depressed, spring, 15,engages sprintf, 17, thereby grounding the vertical side of the line forthe operation of the ringing relay in the connector switch.

Referring now to Fig. 3, the two limbs, V and R, of' the subscribersline may be seen entering at the left of the sheet. These limbscorrespond with those shown in Fig. 2, leading from the mechanism at thesubscribers station. The bridge cut-olf relay, CO, has one terminalconnected to the live pole of the battery, B, of about 50 volts. Theother terminal is connected to the contact, la; this is a portion ofwhat is" known as the oil normalswitch, the office of which is to breakcontact between springs, 1a and 2a, and make contact between 2a and 3a,whenever the shaft of the selector is moved from its normal position;this switch will be actuated at the first vertical motion of the shaft,remaining so actuated until the switch has been wholly released andrestored to normal. The relay, CO, will therefore be disconnected fromanything except one pole of the battery, B, whenever the switch is ornormal. The springs, 4a, 5a and 6a, are controlled by the relay, CO;they are normally in contact with each other, the result being that aconnection is made between the live pole of the battery, B, and therelays, VR and RR. The other terminal of the relay, VR, connects withthe contact point, 26", of a device known as a side switch. This sideswitch is a device operated in a manner yet to be described, and which,in my system, has four levers, 25a. 25h, 25e, and 2. d, adapted to movetogether as a unit, but connected to four distinct parts of the circuit.The side switch mechanism is illustrated in Figure 8 and the sami.lreference characters are used, Where possible, as those used in theother figures. No attempt is made, in this igure, however, to illustrateassociated parts which are not directly concerned in the operat-ion ofthe side-switch- Thus, for example, the private magnet, PM, is shownwithout the contacts 9a, 10a and 12 which, in fact, are associated withthis magnet as shown, for example, in Fig. 3. The rotatably mountedshaft, 201, carries the side-switch levers 25a, 25h, etc. only two ofwhich are shown, however. The associated contacts are shown at 26a, 27,28a, and at 26h, 27h, and 28". The arm, or lever, 202, having atriangular cross-section is rigidly mounted upon the shaft, 201. Theprivate magnet PM is provided with an arn'iature, 203, pivoted at 204-and having an arm 205, extending toward the lever, 202. A spring, 211,co-operating with a spring arm, 212, tends tocause a rotation of theside-switch shaft and its switch arms in the direction of the arrow,213. Thus upon the energization of the private magnet PM, the arm, 205,is depressed and this causes the tooth, 206, on the escapement arm tostrike the top of the tooth, 210, on the spring, 208, thus forcing thespring out of engagement with the escapement arm, 202. The face of thetooth, 206, is only slightly to the left of the face of the tooth, 210,so that the substitution of the tooth, 206, to retain the escapement arm202 in its position in place of the teeth 210 does not permit anymaterial rotation of the side-switch shaft due to the tension of thespring, 211. TVhen, however, the de-energization of the private magnet,PM, permits retraction of the armature, 203, due to the influence of thespring, 214, `the face of the tooth, 210, will not engage the frontsurface of the escapement arm, 202, and this arm and shaft will bepermitted to turn to the left under the influence of the spring, 211,until it strikes the vface of the tooth, 209. So, also, a subsequentenergization of the private magnet, PM, will `first cause the tooth,207, to be substituted for the tooth, 209, to retain the sideswitchshaft in its position, and then upon the de-energization of the privatemagnet the side-switch shaft will be caused to move a step further inadvance. The wire, 215, which is connected with the arm, 212, passesthrough a hole in the rigidly supported `guide, 216, and is providedwith an adjustable stop` 217, by means of which the forward rotation ofthe side-switch shaft limited.

The restoration of the side switches and the shaft upon which they aremounted to their normal position is brought about by the energizationand subsequent de-energi- Zation ot' the disconnect-magnet, DM. Inaddition to the mechanism associated with this magnet for causingrestoration of the shaft, 31, to its normal position, the armature, 21S,of the magnet, DM, is provided with a catch. 219. The armature ispivoted at 220 and returned to its normal position by a comparativelystiff spring, 221. The wire, 21:7, which is quite springy, is providedat its end with a very thin, flexible plate. this plate having asuitable opening at 223. The vertical magnet, VM," is equipped with anarmature, 224.-, pivoted at 225. and provided at its extremity with acatch. 220. The energization of this magnet, VM, raises the armature,224, and by means of the catch, 226, it raises also the plate,disengaging it from the restraining influence of the catch, 219, andmaking the rotation of the side-switch shaft 201, subject only to theoperation ofthe escapement associated with the private magnet, PM.

The restoration of the selectorl mechanism upon the energization andde-energization of the disconnect-magnet, DM, restores the plate, 222.to the position shown in Fig. 8. When next this particular mechanism iscalled into service the first energization `of vertical magnet, VM,immediately releases the plate, 22.2, from the catch, 219, and puts theside-switch under the control of the escapement associated with theprivate magnet, PM. The normal position of this side switch is thatshown in Fig. The described contact of the lever, 25", upon point, 26",operates to connect the vertical rela),v with the 'vertical wire, V;similarly, contact of the lever, 25, upon the point, 26C, connects therotary relay with the rotary wire, R; ground contacts upon the verticalwire, therefore, as caused by the subscriber instituting a call, willoperate the vertical relay by as many impulses as there are digits inthe left-hand figure `of the called subscribe1"s number. This will causeas many contacts between the' springs, 7a and 8a; the resultl will be anoperation of the vertical magnet, VM, in as many impulses, the circuitbeing from the live pole of the battery.` B, 'through the verticalmagnet, VM, the contact between the springs, 9 and 102L `of the privatemagnet, PM, and t0 ground bv contact between the springs, 7

and Sn. The shaft, S, will be lifted by this action, as many steps ofits ratchet as there lwere ground contacts, and will remain lifted. As aseries of vertical impulses is always followed by one rotary limpulse,this latter `will cause a closing of the vcontact of the rotary relaybetween-springs, 11EL ,and

8a; the private magnet, PM, of which one terminal is connected to thelive pole of the battery will t-hus be energized. The armature ot this',iagnet, by drawing up and falling hack again, will operate the sideswitch, as Yit is this forward and back motion of the armature of' thismagnet which controls the side switch through an escapement associatingthese parts together; but the move ment of the side switch forward onestep, acts to move all four of its levers; the movement of the lever,25a, connects to ground one of the terminals of the rotary magnet, Rlvl;the other terminal of' that magnet is connected through its own armaturecontact to the live pole of the battery. rit the point, 30, associatedwith the rotary magnet, RM, is a contact which is broken just at theclose of each stroke of the armature of this magnet, somewhat after themanner of the Vfamiliar vibrating electric bell. The operation oit theside switch in making this rst step, therefore, will, so far as thisfeature concerned, cause the rotary magnet to make a series of strokes,and these will rotate the shaft through the agency of the rotaryadvancing pawl. As each impulse of therotary magnet causes the wipersupon the rotary shaft to make successive connections with the contactpieces in the bank, the wiper, 33, will connect with the contacts of theprivate wires of' trunk lines, which are or are not busy. lf the trunklines are busy, the private contacts made by the wiper, 33,

'I will be grounded, in which case the private magnet will form acircuit from the battery, B, through its winding, through the contact,27d, of the side switch to the lever, 25d, through the winding of thedisconnect relay, DR, the wiper, 33, to the contact which is grounded onthe private wire of the busy trunk line. This will Cause the armature ofthe private magnet to be retained and will thus prevent a movement ofthe side switch from its middle to its last position. The disconnectrelay, DR, will not, however, 4be operated because it is of so iew turnsthat the current it may receive while in series with the private magnet,will not be sufficient to actuate it. When the wiper. 33, makesconnection with the contact piece of the private wire of a trunk linewhich is not in use, no ground will be found upon that contact, theprivate magnet will be released instead of being held as last described,and this operation will permit a second motion of the side switch, thuscarrying the levers on to the extreme position. This final motion of theside switch accomplishes four results: First, because of the removal of'the ground from the lever, 25a, the rotation of the shaft will bestopped because lof the opening of the circuit of the rotary magnet, RM;second, the two line conductors, V and R, which until this time had beenconnected to their respective relays'ffliJ and Rit, are now disconnectedfrom those relays, and third, they are eXtendedthrough the wipers. 3land 32 to the conductors, and 36; and it is to be noted that these lineconduc tors are now free of any bridge or any series magnet windings;fourth, by the movement of `the lever, 25, upon the point, 28d, a groundis placed upon the private wiper, 33, through the winding of thedisconnect relay, Dit. This serves to hold the selected trunk line busyagainst the stoppage of other selector switches upon it, because it isthe presence of' ground which prevents such a selection of the trunk.

Reference has been made to the off nor-- mal switch, and to the 'factthat its operau tion disconnects the cut-ofi relay, CO, from thecircuits. lts further operation is bv cont-act between the spring, 2a,and the point, 3a, to ground, through the private conductor of' theindividual line of the selector in question. Such a ground serves toprevent a connector from completing a connection with the line, and thisneeds to be so because a line should become busy as soon as its firstselector a tempts a connection with another line.

But the trunk line composed of the conductors, 35 and 36, is one whichextends to a second selector. Referring to Fig. 4, it will be seen thatthese conductors enter the mechanism of the switch quite as was true inthe case of the first selector. W' ith the side switch in the normalposition, vertical impulses over the wire, 35, will operate the verticalrelay, and in turn the vertical magnet, the connections and sequencesbeing exactly as described ior these operations with reference to thefirst selecfor. rlhe first vertical. motion of the shaft in response toimpulses from the vertical magnet, operates to close the contact in theoff normal switch, 37, allowin(Y current to flow from the battery, B,through the lamp, 38; this lamp simply signied that this selector, orone of a group if the lamp be made common to a number of other contactsin parallel with the parts 37, has 0perated, and has no function insetting up the connection between lines. As the series of' verticalimpulses ceases, and is followed by an impulse through the rotary relay,its closure of the spring, 39, upon the ground contact, 40, causescurrent to flow from the battery, B, through the winding of the privatemagnet, PM', drawing up the armature thereof. Consequent circuitchangesv of the springs, 42, 43 and 44, resulting from this armatureaction, need not be here considered. The important thing which happensis that the drawing up and falling back of the armature ofthe magnet,PM', allows the associated escapement to advance the side switch onestep. This brings the rotary magnet, RM', into action by allowingcurrent to flow from the battery, B, through the windings to the groundon the point, 47a. iiiinultaneously, the levers, if", 45@ and 45d, moveto their respective contacts, t7", 47C and 4:.71. Dueto the presence ofthe contact, 5%?. associated ivith the rotary magnet, Rld, the circuitof this magnet will be opened by the stroke of its own armature asdescribed with reference to Fig. 3, and a series of impulses willadvance the contact wipers, 49, 5t) and 5l, step by step over thecontact pieces of that row of the bank. As soon as the contact wiper,5l, engages a con tact of the private wire, 53, which is not grounded,the private magnet, PM, will release its armature, although it had beenheld since the beginning of the described rotation of the wipers. Thisrelease accomplishes through the escapenient, the second step of theside switch, advancing the arms, Li5 lto 45d, to the last position,breaking the ground contact between 4.5 and 47a, stopj ping furtherrotation of the shaft, as caused by the rotary magnet, RM. The actionsof this last described movement of the side switch, are to .stop therotation as indicated, to extend the line conductors to the wipers, 49and 50, and to place a ground through the contact of the lever, 45d,with point. 48d, through the winding of the disconnect relay, DR, andthe wiper, 5l, upon the conductor, and the various contact pieces of theprivate wire, It will be noted that the operations, and the `conditionsin which `the selector is left, are quite identical with relation `tothe first selector illustrated in Fig. 3.

In Fig. 5, illustrating the third selector, the trunk conductors, 57 and58, may be considered to be extensions of the conductors.I 54 and 55,shown in Fig. 4, as leaving the second selectors. Similarly, the privateconductors, 59, may be considered as an extension of 'the privateconductor, 53, shown iii-Fig. 4, as leaving the second selector. Thethird selector differs from the first and second selectors in that thevertical and rotary relays are permanently bridged upon the trunkconductors, 57 and 58. In a normal condition the conductors, 57 and 58,are open at their respective levers, 60c and 60d of the side switch.Upon the actuation of the mechanism at the subscribers station in amanner corresponding with the third digit of the called number. groundcontacts upon the vert-ical wire will cause current to flow from thebattery, B, through the vertical rela-y, to the line, in as manyimpulses as the digit requires. This, in a manner similar to thatpreviously described, will make contact between the spring, 64, and theground contact, 65. This will cause current to flow from the battery, B,lever50b, contact. 6l",

through the vertical magnet, VM2, and the closed Contact betweensprings, 66 and 67, of the private magnet, PM2, to ground. The shaft ofthe third selector will thus be lifted by impulses until it is oppositethe proper horizontal row. The ground impulse upon the rotary wire,which as usual succeeds the vertical series, will cause one movement ofthe rotary relay, RR2; this, as before, by virtue of current flowingfrom the battery, B, through the private magnet, PM2, to the groundcontact of the spring, 68, with the ground Contact, G5, will cause an attraction and release of the armature of the magnet, PH? The breaking andmaking of contacts by the action of this armature, need not be hereconsidered,- the important thing is that the forward and back motion ofthe armature in question acts, through the escapement, to advance theside switch one step, causing the contacts between the arms, 60a to 60e,to be placed upon the points, 62 to 62e respectively. As the contact,G2, is grounded, current will flow from the battery, through the rotarymagnet, BH2, and its own interrupting Contact, to the lever, 60a, and toground. This will cause a rotation of the shaft quite as described withreference to other switches, which will continue until the privatewiper, 72, makes contact with a contact piece of the private wire, 73,of a trunk line which is not in use. As the contact of the pr' "ate wireof a trunk which is not in use has no ground upon it, the rotarymovement of the shaft will cease because of the release of the armatureof the private magnet, which armature is held attracted as long as theprivate wiper, 72, shall make connections with contact pieces connectedwith the grounded private wires of busy trunks. This arrest of therotation of the shaft is due to the fact that current from the battery,B, through the private magnet, PM2, the Contact (S29, lever, 60e, to theprivate wiper, 7:2, may flow when a ground is encountered by that wiper,and may not otherwise; so that when a ground is not found, thc armaturepreviously attracted falls away, advances the side switch to its thirdposition, removing the connection between 62 and 60a, which has set therotary magnet, RM2 in action. This third posit-ion of the side switch inaddition to stopping the rotation of the shaft, extends the trunk.conductors, 57 and 58, through to the wipers, 7 O and 7l. Further, itacts to place a ground upon the lever, 60e, by contact with the point,63e, and this grounds the private trunk conductor, 73. The elfect ofthis is to guard this trunk against being selected by any other thirdselector attempting to establish another connection.

It is to be noted that the condition of the extended connection is atthis time that of having but one bridge upon it, this being thatprovided by the bridge of the vertical and rotary relays, VB2 and RRZ,in this described third selector.

. In Fig. 6, are shown the conditions of the connector. It is to aswitch of this type that theY connection now is led, the trunkconductors entering the switch on the wires, 76 and 77; the verticalrelay, VRS, and the rotary relay, BB3, forming a permanent bridge acrossthe trunk co-nductors. In respense, therefore, to the impulses sent bythe subscribers instrument for selection relative to the fourth digit ofthe called number, the vertical relay will be energized by current fromthe battery, B, through its winding to the wire, 76. At the same timethe relay, VR2, in the third selector, will be operated, but, due to thefact that the side switch shown in Fig. 5, has completed its cycle. ofconnecting operations, these vertical impulses will produce no effect inthat switch. In the connector as shown in Fig. 6, however, the verticalrelay movements will cause steps on the part of the vertical magnet,VMS, by virtue of current from the battery, B, through the verticalmagnet, the co-ntact, 81, to the lever, 80, of the side switch, thesprings, 84 and 85 of the magnet, Pil/13. the spring, 86, to the groundcontact, 87. These vertical impulses will cause the shaft of the switchto be lifted by successive steps. As usual, the series of verticalground contacts at the substation will be followed by one rotary groundcontact, the result being, through the agency of the magnet, PMS, toadvance the side switch one step exactly as described with reference tothe other switches. The results, however, of moving the sideJ switchlevers to their second positions, are not eX- actly as before described.The movement of the lever, a, to the contact, 82a. puts the rotarymagnet RM3, in the relation to the vertical relay, VB3, previouslyoccupied by the vertical magnet, VMS. This being so, the next series ofcontacts at the substation between the gro-und and the vertical wire,causes as before, successive contacts between the springs of thevertical relay, VRS, and the rotary magnet, RMS, which is now actuated,stepping the shaft through as many horizontal steps as are required bythe units in the fifth and last digit of the called number. The wipers,88 and 89 thus make conu tact with two terminals of the line of thecalled subscriber, although the lines of the calling and calledsubscribers are not as yet connected together. The succeeding rotaryimpulse which always accompanies the series belonging to any digit,actuates the relay, BB3, to make one contact upon its spring, 91, andthe ground contact, 87. Bv virtue of `current flowingq from the battery,B, through the magnet, PMS, and this contact between 91 and YV87, thearmature o-f PM-3 is attracted and then released. This operates the sideswitch through the escapement, advancing all the levers to the thirdposition. The results are three:

First, that the line conductors, 7 6 and 77, which have in series withthem the condensers, 96 and 97, are extended by contact respectively ofthe levers, 80b with 88h, and 80c with 83e, tothe contacts o-f thespring, 92 with 102, and 94E with 95 respectively, of the ringing orcalling relay, GR, and thence to the wipers, 88 and 89, respectively.This establishes a connection of the line of the calling subscriber withthat of the called subscriber, as in this instance the conductors, 100and 101, leading from the contacts, 98 and 99, are not a trunk line, butare a line to the called subscriber, via his first selector, yet to bedescribed.

The second result of the side switch mo tion is that the lever, 80a, inmoving upon the contact, 83a, entends the conductor which it carries toone terminal of the winding of the calling relay, Clt; the otherterminal of that winding is connected to the battery, B. At thisjuncture, the calling` subscriber presses the ringing button of histelephone, which, vas before described, places a ground upon thevertical wire, this being in Fig. 6 designated as 76. Current from thebattery, B, through the relay, VRS, to this ground at the substation,will actuate the relay, VB3, operating the winding of the calling relay,Clt, the path for current being from the battery, B, through the windingof the relay CR, by the side switch contact of 88 with 80a, and thecontact of the private magnet springs, 84 witl1r85, the spring, 86, thecontact, 87 of the relay, VRS, and thus to ground. The operation of themechanism of the relay, CR, is to disconnect the springs, 102 and 95from theirrespective contacts, 92 and 91, bringing them into contactwith the springs, 103 and .93, these being the terminals of a ringinggenerator, 104, or other convenient source of ringing current. As thecalled subscribers line is immediately connected to the springs thusmoved, calling current will be sent over his line. Upon his response,conversation may ensue.

The wires, 100 and 101, in the consideration of Fig. 6, have been spokenof as extending directly to the station of the called subscriber. Byreference to Fig. 7, in which 127 and 128 are the extensions of theconductors, 100 and 101, the lines, 129 and 130. are to bev consideredas leading directly to the station of the called subscriber. lOtherwiseFig. 7, is a duplicate representation of a first selector, and issimilar to Fig. 3. ln the case of a selector of a called line, however,it is evident that it will not contain at the time of the connection,conditions which result from thecontrol of its station as no call hasbeen made from that instrument;

nor has'the shaft of the switch been moved from a normal position. Asthis is so, the conductor, 131, which is anV extension ofthe privateconductor, 132, of Fig. 6, leads through the closed ofi normal switch inthe contact of springs-,142, 143 and 144, to the cut-off relay, CO. Uponthe completion, therefore, through the act of the connector shown inFig. 6, of a connection With a called line having the mechanism of Fig'.i", ground which is thus applied to the private Wires, 131 and 132, bythe Wiper, 90, will establish a circuit from the battery, B, in Fig. 7,to and through the cut-off relay Winding, CO', through the contacts, 142and 143, operating the cut-ofi relay, and removing the circuits of therelays` VR and RR, from thev line. This will eectuaily prevent anyoperation of the mechanism of the selector, and will keep that bridgeoff the line as is indicated inthe schematic arrangement of the circuitshown in Fig. 1.

The third result of the motion of the side switch is to effect contactbetween the lever, d, and the grounded point, 83d. This places a groundthrough the medium of the Wiper, 90, uponthe private contacts associatedivith the line of the called subscriber, thus preventing anotherconnector from stopping With its Wipers upon the line of the calledsubscriber.

En the operation of this connector switch, as has been described, it wasassumed that at the moment the Wipers, 88 and 89, are carried intoconnection With the contacts, 98 and 99, of the desiredline, that thatline was not busy. lVhen it is remembered that at the moment of themaking of this contact, the side switch was in its middle position, andthat the rotary impulse, about to succeed the series of verticalinipulses, had not yet been given, the operations which succeed thatimpulse, in case the called line is busy, will be understood: In such acondition of connecting with a busy line, the contact Wiper, 90, will bein engagement with the grounded contact of the private Wire belonging tothat line. In these circumstances` a circuit'involving the disconnectmagnet. DMS, is established as follows: From the battery, B, through theWinding of the magnet, DMS, to the contact between the springs, 105 and106, at the relay, RR3 to the contact, 82d, upon which at this momentrests the lever, 80d, to the private Wiper, and thence to ground. Thiswill permit the energization of the magnet, DMS, and its action upon thevertical and rotary pawls will permit the shaftv to return to normalposition, through the agency of its springs and gravity. It is thus seenthat the rotary impulse following the series of vertical impulses whichestablished final connection, acts to disconnect the connect-or switchif the line is busy, or to close the line through for con versation ifthe called line is not busy. In the care of the disconnection by virtueof the line being'busy, the side switch will be restored to its normalposition. The subscriber will not know Whether he has connected with thecalled line or not, and uill, as a natural sequence, press his ringingbutton. This acts to ground the vertical wire` but instead of theresulting operation of the relay, VB3, being, as described, to operatethe calling relay, CR, it will be to lift the Vshaft vertically onestep, the means by which this is done being, as frequently describedhereinbefore, the result of a period of ground upon the vertical wire,as 70 in Fig. G. It may be that the pressure of the ringing button maybe in one impulse or in several, but the effect is only to lift thevertical shaft one step or several as the case may be. If it be liftedeven one step` the oii normal switch, formed of the springs, 10T and108, will close together; and in so doing Will establish a circuit fromone pole of the auxiliary battery, B, through the high speedinterrupter, 109, which is shunted by the condenser, 110, through thelamp resistance. 111, contacts 107 and 108, to the contact Si of theside switch, through the condenser, 96, over the conductor, 76, to thesubscribens instrument, through his telephone, back to the centraloliice and through the rotary line conductor, ultimately reachingthrough the conductor, 77, the relay, FR3, and through its Winding tothe other pole of the battery, B. As the current in question is aninterrupted one, it will find` a path through the circuit described,giving in the subscribers receiver a tone understood by him to mean thatthe called line is busy. In response to this signal he will hang up hisreceiver, causing disconnection of the other switches used in theprevious operations, of which disconnection the sequence of events is asfol/lows:

By reference to Fig. 1, it Will be seen that in afcompleted connectionthere are only tivo permanent relay bridges upon the builtup line, so`far as any control ofthe calling station is concerned'. These are at thethird selector and at the connector. It is evident that if disconnectionis to take place through the agency of the bridged relays.` it cannot beinstituted by the use of the relays at thi` first and second selectorsconcerned in the connection, nor at the first selector of the line whichis called, but must be instituted by functions of the connector or thethird selector, or of both. So far as the connector is concerned, as ithas its vertical and rotary relays, VB3 and BB3, permanently in bridgeand connected to the batterj, B, the act of hanging up the telephonereceiver and connecting together and to ground the tivo sides ofthe lineWill energize both of these relays, as has been described in theprocesses of connection. The rotary relay will, as usual, operate themagnet, PM3, because of current from the live pole of the battery, B,through the magnet, PMS, and to ground by Contact of the springs, 91 and87. The magnet, PMP', will effect contact between its spring, 85, andcontact, 112, establishing a circuit from the battery, B, through thedisconnect magnet, DMS, to the spring, 86, and thence, through thesimultaneous operation of the relay, VRS, toground by contact with thespring, 87. This current will energize the disconnect magnet, Dl 3, andwitl draw the vertical and rotary pawl-s, allowing the shaft to returnto its normal position by action of its spring and gravity.

lith respect to the disconnect actions in the third selector, referenceto Fig. 5 will show that in this switch also, the vertical and rotaryrelays, VR2 and RRZ, are in permanent connection with two sides of theline, and with the battery. At the same instant when the ground wasapplied at the substation to the two sides of the line, releasing theconnector, the relays, RRZ, and VR2, operate in precisely the samemanner, energizing the disconnect magnet, DM2, Fig. 5, withdrawing thepawls from the shaft and allowing it to return to normal position. Atthe moment of the energization of the disconnect magnet marked DM2 inFig. 5, 'a contact was made by that magnet between the springs, 113 and114. This is by way of being a relay function of the disconnect magnet,DM2, and is the-only feature wherein the disconnect portions of themechanism shown in Fig. 5, differ from those which have been describedwith reference to Fig. 6. The closure of the contact between springs,113 and 114, establishes a circuit bacl: over the private conductor, 59,to the second selector. Current results, flowing from the live pole ofthe battery, B, through the resistance, 115, of about 100 ohms, over theprivate wire, 59, in Fig. 5, over the private wire, 53, in Fig. 4, tothe contact which is in connection with the private wiper, 51, throughthe disconnect relay, DR', to the lever, 45d; and as this is in itsfinal position, to the ground at contact, 48d. The winding of thedisconnect relay, DR', is of low resistance and few turns, and thereforedid not develop sutlicient energy within itself to be actuated in thecircuit in which it was previously placed in series with the magnet,PM', of its own switch. It will, however, be actuated by being placed inthe circuit which I have just described. and will close its contacts,116 and 117. I find a convenient resistance to which to wind the relay,DR', to be about 8 ohms. The effect of closing together the springs, 116and 117, willbe to establish a circuit from the battery, B, in Fig. 4,through the disconnect magnet, DM', springs, .116 and 117, to

ground, operating the magnet, DM', the release of its armature, actingto withdraw the vertical and rotary pawls from the shaft, permitting itto return to its normal position by the action of its spring andgravity. But the magnet, DM', similarly to the magnet, DM2, is providedwith a con* tact so that it acts not only as a disconnect magnet, but asa disconnect relay, as well. Its contact, composed of the springs, 118and 119, assists in establishing a circuit from the live pole of thebattery, B, through the resistance, 120, conveniently of 100 ohms, overthe private wire, 121, to the private wire, 56, shown in Fig. 3, asassociated with the first selector. The sid-e switch of this lirstselector, being upon its third contacts, the circuit from the privatewire, 56, will be extended through the wiper, 38, and-the disconnectedrelay, DR, to ground, via the lever, 25d, and the contact, 28d. Therelay, DR, being energized will close contact between its springs, 122and 123, establishing a circuit from the live pole of the battery, B,through the disconnect magnet, DM, to ground. The disconnect magnet willthus attract its armature, not shown in the drawing, and its subsequentrelease will withdraw the vertical and rotary pawls from the shaft,allowing it to return to normal position, through the agency of itsspring and gravity. The disconnect relay, DR, of this switch, isprovided with a winding of few turns, and low resistance, the latterbeing practical if about 8 ohms, adapted as described with reference tothe second selector, to operate in series with the battery and aresistance of about 100 ohms, but not to operate in the previouscondition of being in series with the winding of the private magnet, PM.

It will be observed that all of the switches have been released, andthat the condition is now normal and ready for the setting up of a newconnection.

For the purposes of giving service between toll or interurban lines, andlocal lines of an automatic exchange, it is sometimes necessary toestablish trunk lines between a toll board and the automatic system. Asatisfactory method of doing this is to terminate such trunk lines inspring jacks upon the toll board, and in lirst selector switches in theautomatic apparatus. The toll operator may thus, by means of suitablelreys or switches, send impulses to the selector, which will cause it,and others with which it. will associate itself, to set up any desiredconnection with a called subscribers line. A subscriber so called by thetoll opera'tor may desire to release his line from a toll connection, ormay desire to 'signal the toll operator. Fig. 6 illustrates how this maybe done. Assuming that it is desired by the called -subscriber todisconnect his line from the toll board, and knowing that at such a timeof the connection the side switch will be upon its third position, theoperations are these: The called subscriber moves the dial ot hisinstrument as if to cal'l adigit ot a desired number, and then hangs uphisreceiver. The movement ot the dial first mentioned serves toestablish ground connection between the springs, 7, in Fig. 2, and thehanging up ot' the receiver, the connect-ion between the springs, 12, 13and 14, grounding both sides ofthe line. This will ac'tua'te both therelays, BS and BR, in Fig. 6, the circuit in both cases being tracedfrom the battery,B, through the relay in question, over the side of 'theline with which it is associated, and to the ground at the substation.These relays being i operated, the springs, 124, 125 and 126 will beclosed togather. The spring, 126, being grounded by 'this joint actionof the relays, which would not have been true if relay,fBR, `alone hadbeen actuated, a circuit will be established trom the battery, B,through the magnet, DMS, 'to ground, attracting the armature of thisdisconnect magnet, withdrawing the vertical and rot-ary Apawls tromtheshait, allowing it to returnto its normal iposition through theagency ot its spring and gravity. Y

i Itwill be seen that the described actions on the part of thesubscriber would have secured release ot his line on the part oftheconnector, however the connection had been setup. f' i v tIt it shouldbe desired by the subscriberfto give ay signal tothe toll board for the`purpose of indicating further instructions on his part while his linewas being held by the toll operator, his manipulation `would he to presshis ringing button, which `would ground `the conductor, 100, andestablisha circuit as follows: From the batter B. through the relay, BS,lever, .80", an the contact, 83 of the side switch, the springs,

92 :and 102, of the relay, CR, the wiper, 88, and contact, 98, of theconnector switch. The relay, BS, will operate, establishing a circuit asfollows: From the battery, B, through conductor 150 to 4:aurelay or'other signal 151 on the toll board T, through conductor 152 tothespring, 125, and the con-' tact, 12st, to ground. This will energize therelayer' signal upon the toll board during' the `pressure oi' the buttonat the subscribens stat-ion, indicating that he desires attention on thepart of the toll operator.

Referring to Fig. 1, it will be seen that in addition to showing therelation of the vertical and rotary relays to coiuluctorsotithc lineproper of each ot' lthe iive switches involved in a completedconnection, the 4portions ottheprivate wire, P, are indicated to extendtroni each switch group to the succeeding one, The result of thisarrangement is that three conductors are required in each trunk whichentends 'from switch group to switch group, and my inventioncontemplates such an arrangement, which is not a disadaf'antage oteconomic importance in an exchange which has all of the lines ot itssubscribers centering in one oilice, vor in a p'mrality of ofiiccs whichare located very near to each other. The private wire which forms thisthird conductor in the sections .from switch group to switch group,serves, as has been described, to establish busy test conditions fort-he prevention or" connection with trunk lines which are in use, and inaddition serves `t-he purpose oi' enabling one switch at which a bridgeis present, to secure the operation of the release magnet at anotherswitch at which no bridge is present.

lt will be seen from a consideration of the foregoing description andthe illustrations to which it rcicrs, that each of the `line relays,such as VR and RR, VR and RR', etc., are means at the central oil'ice bywhich the subscriber controls the operation ot the various selectors andconnectors. The magnets ot these controlling relays may, therefore, betermed controlling magnets, and it will be seen that in all cases theyare normally bridged across the circuit of the subscriber-s line or ofthe trunk line to which 4the corresponding selecting switch belongs. lnthe case, however, of some of the selecting switches, and moreparticularly of those connected with Athe subscribers lines forselecting trunks, and those of the `trunks selected by said subscribersselectors, these controllingmagncts are cut oit by the action oi theside switch so as to be ineiifective for further use after the selectingswitches to which they belong have yperformed their' functions otselecting and connecting with the succeeding trunk lines. By this meansthe combined circuit between two subscribers 4is relieved of some ot thebridges that would be' placed across it were the controlling magnets ofall the selecting switches involved in making the connection le'litpermanently bridged. Unless other means are provided these selectingswitches would be left without means tor releasing them at the close otthe conversation, since the two controlling magnets have in the pastformed the only means tor bringing about such release. My system hereindescribed, provides against this diiliculty, and makes pos sible thereleasing of those switches which are deprived ot their normal bridgesby means of a separate wire associated with each ot the various trunklines, over which wire an electrical impulse is sent which, eitherdirectly or indirectly, energize's the release magnet of 4the switch orswitches in vo'lved in the connection from which the normal bridgeshavebeen removed. lnother words, 'I provide uiieans `whereby one selectCil Cri

ing switch at which a bridge is present is adapted to bring about theoperation of the release magnet of one or more other switches involvedin the same connection, at which no bridge is present, this beingaccomplished over the third or p rivate wire.

I do not wish to limit myself in all respects tothe exact details andcircuit connections here shown. For inst-ance, while I- have described asystem in this applicationY with particular reference to an eli-- changewherein the subscribens numbers are composed oi' five digits, it isobviously applicable to apparatus and mechanisms re, quired by systemshaving a greater or a less. number of digits. Neither do I wish to limitVmyself as to the number of selector switches involved in a connectio-nthat shall have their normally bridged ycontri'illing magnets removedfrom connection with the line dur-v ing a connection. It is obvious thatthere will be conditions where only one of said pairs of controllingmagnets need be'removed, and in other cases it may be desirable toremove an even `greater number than in the system of this application.It is also obvious that many other changes may be made without departingtrom the spirit oi my invention.

Having thus described my invention, what I claimV as new and desire tosecure by Iictters Patent, is:

l. In a telephone system, a metallic circuit line, a substationthere-for, a selector for said line, selecting contacts in saidselector, a pair of controlling `magnets ing the second of said magnetsto cause the movement of said selecting contacts in another direction, aside switch adapted to disconnect botli ot said magnets and said line,and meanscontrolled by said second magnet for operatino` said sideswitch to disconnect both of saiy magnets from said line, substantiallyas described.

2. In an automatic telephone system, a metallic circuit line, asubstation therefor, a selector at the central oliice for said line,selecting contacts in said selector, a pair of controlling relays forsaid selector bridged across said line, a source of current adapted toenergize said relays overV the limbs of said line, means at thesubstation for. closing the circuit of one of said relays 'for causingsaid selecting contacts to move in one direction, means at the centralof- Ytice for moving said selecting contacts 'in rent, a pair ofcontrolling relays normally` connected between the limbs of said lineand said source of current, means under the control of one of saidrelays for causing said selecting contacts to be moved in a longitudinaldirection, a side switch, means under the control Aof said side switchfor causing said selecting contacts to rotate, contacts on said sideswitch adapted to disconnect said pair of relays Yitrom the limbs ofsaid line, and means under the control of said second relay to cause theoperation of said side switch, substantially as described.

4. An automatic telephone system comprising a temporarily establishedcircuit, a pair of switches having contacts serially included in saidcircuit, an electromagnet controlling the release of. one lof saidswitches, a third conductor independent ot the talking circuit extendingbetween said switches, a iesistance coil in the other switch, and meansat the latter switch for connecting said elect-romagnet and saidresistance coil in series with said third conductor or causing therelease of the iirst switch.

5. An automatic telephone system coniprising a temporarily establishedtalking circuit, a selector relay bridge temporarily disconnected or cutoiit from said circuit, a selectorwiper controlled by said bridge, aconnector relay bridge retained across said circuit for releasingpurposes, together with selector and connector releasing means, aresistance coil associated with the connector and included in a releasecircuit through said wiper controlled by the connector relay bridge.

6.- An automatic telephone system coinprising a temporarily establishedtalking circuit, a selector relay bridge temporarily ,disconnected orcut off from said circuit, a y,selector wiper controlled by said bridge,a .connector relay bridge retained across said circuit for releasingpurposes, together with selector and connector releasing means, a

resistance coil associated with the connector State of Illinois.

BERT @UNI-IMEI,

